1. Statement of the Technical Field
The inventive arrangements relate to Microelectromechanical System (“MEMS”) and methods for forming the same, and more specifically to differential inductors for MEMS devices.
2. Description of the Related Art
MEMS is a technology of very small devices typically between 2 micrometers to 2 millimeters in size. The MEMS devices can include one or more components between 1 to 100 micrometers in size. Conventional MEMS devices are fabricated using molding techniques, plating techniques, wet etching techniques, and/or dry etching techniques. Various materials can be used to create the MEMS devices. Such materials include silicon, polymers, metals and ceramics.
Radio Frequency (“RF”) filters typically occupy a relatively large amount of space in an RF system (i.e., >25%). As such, it has been desirable to miniaturize RF filters via MEMS technology. RF filters may comprise varactor devices, such as Gap Closing Actuator (“GCA”) varactors. GCA varactors generally operate on the principle of electrostatic attraction between adjacent interdigitating fingers of a drive comb structure and a movable truss comb structure. That is, motion of the truss comb structure can be generated by developing a voltage difference between the drive comb structure and the truss comb structure. The voltages applied at comb structures are also seen at the interdigitating fingers, respectively. The resulting voltage difference generates an attractive force between the interdigitating fingers. If the generated electrostatic force between the fingers is sufficiently large to overcome the other forces operating on truss comb structure (such as a spring constant of a resilient component), the electrostatic force will cause the motion of the truss comb structure between a first interdigitated position (resting position at a zero voltage difference) and a second interdigitated position (position at a non-zero voltage difference) among a motion axis. Once the voltage difference is reduced to zero, a resilient component (e.g., a spring) restores the position of the truss comb structure to the first interdigitating position.
RF filters typically comprise RF inductors built using thin films disposed on the substrate (e.g., Silicon or Silicon Germanium). Such RF inductors are typically limited in their performance which is proportional to their Quality (“Q”) factor. The limited performance of the RF inductors is a consequence of parasitic effects and dielectric losses from the substrate and is a function of frequency. As the frequency increases, more loss results due to coupling of the electric field through the substrate, instead of between the windings of the RF inductor.